The present invention relates to a power connector apparatus having an integrated surge arrestor means and particularly adapted for connection of the power cable to a submersible motor and the like.
Electrical power circuits may be subject to transient high voltage surges which can seriously damage the system components. Electric motors and particularly submersible well motors may be subject to high voltage surges if lightening strikes the supply system, for example. Submersible motors are used in combination with an integrated pump unit for pumping of water and other liquids from within a confining well or supply. Deep water wells include a drilled ground opening within which a well casing is secured. A submersible motor-pump unit consisting of a lower motor and an upper pump of a size is adapted to be dropped into the well, with a discharge pipe extending upwardly and providing a support structure. Generally the motor-pump unit is an elongated cylindrical assembly having an external diameter somewhat less than that of the well casing. A power cable lower end is connected to the motor and the cable is secured to the well support piping and extends upwardly out of the well to a suitable power supply. For domestic water applications, wells on the order of three hundred feet are not unusual. For commercial and institutional installations, the well may be much deeper.
The submersible motor is thus located within the lower end of the well and is not conveniently available for repair and servicing. Although submersible motor-pump units have a long operating life, generally substantially in excess of ten years, the motors operate in an adverse environment and are subject to various damaging events. The motor is rated for a maximum operating voltage and any abnormally high voltage, even of a relatively short period of time may damage and/or completely destroy a submersible motor. For example, if a lightening strikes the power supply and travels down through the cable to the motor, the stator winding of the motor will almost surely be destroyed. Replacement and/or servicing is not only inconvenient but expensive. Submersible motors are therefore presently almost universally provided with a surge voltage spark gap or arrestor which will bypass any abnormally high voltage around the motor winding and directly to ground. Although various systems have been suggested, a spark gap assembly is coupled to the motor leads within the motor. In the presence of any abnormal voltage condition of a level sufficient to damage a properly operating motor, the voltage is sufficient to break down the air gap between the lead and the ground member and a spark discharge is created to bypass the high voltage transient to ground. An arrestor unit includes a sealed can having a semi-conductor element located in spaced opposed relation to a disc member connected to the motor connecting leads or terminals. The air gap is enclosed by the case which is mounted in and connected directly to the motor casing, which in turn of course is directly grounded through the well water. Once the air gap is broken, a low resistance path from the lead to the ground is established. The surge voltage and current is then diverted from the motor winding directly through the resistance path to the ground. Such units provide a satisfactory functional protection of the motor.
Submersible motors may be of either a two-wire or a three-wire power supply system. Thus, such submersible motors generally are single phase induction motors and generally include a separate starting phase winding with a switch means for selectively disconnecting of a start winding after the motor reaches operating speed.
For example, U.S. Pat Nos. 3,997,232 which issued Dec. 14, 1976 and 4,053,196 which issued on Oct. 11, 1977, discloses a gap arrestor system incorporated directly into a connection assembly within the submersible motor structure. The surge arrestor unit consists of a multiplicity of parts including a disc-like metal member having three equicircumferentially spaced openings. The metal member is mounted in a cavity within the motor stator, with one motor lead terminal passing through each of the openings and in spaced relation to the member to form spark gaps. The connector assembly is sealed such that the gaps are sealed and protected from any surrounding environment. If a surge voltage is encountered with the motor in its operating position, a spark breakdown occurs and provides a short circuit path directly to ground. Another well known gap arrestor unit which has been used includes a separate canned unit for each lead having a disc member coupled to the power terminal and housed within a conductive can. The unit is located within a potted motor stator compartment and grounded to the motor end cap as shown in U.S. Pat. No. 3,849,704 which issued Nov. 19, 1974. Such devices have a finite life and must be replaced after a number of breakovers. Thus, each spark over tends to distructively burn the electrodes. A similar unit has been suggested in which a relatively heavy disc of silicon carbide is supported in the can by a plastic support and serves as the one spaced electrode. Such separate arrestor structure for each lead is expensive and reduces the economic feasibility of the approach. As a result, the less expensive individual spark gap system has generally been used.
Incorporation within the motor assembly in accordance with standard practice, particularly as a part of a multiple motor part connection assembly, is not particularly adapted to convenient low cost assembly, service and the like. Further, the limited available space for a releasable connector to the top of the motor has resulted in extended leads from the motor. The continuous leads from within the motor are spliced to a flexible cable. However in an oil filled motor, the stranded wires tend to act as a wick tending to draw the oil from the motor, which can be eliminated by the use of a sealed connector means. As noted, the surge arrestors have a finite life and may require replacement. With the surge arrestor incorporated into the motor structure, it is also difficult to properly test the motor during manufacturing. Thus, it is desirable, for example, to subject the motor to a high voltage limit test. With the surge arrestor in place, it is difficult to provide the desired testing of the motor winding and insulation. The surge protective system is advantageously constructed so as to provide universal application both to two-wire and three-wire motors.